International travelers may pick up AMR genes from different destinations

According to new research published in the Genome Medicine journal, travelers abroad may contract bacteria and other vectors with genes that confer antibiotic resistance, which linger in the travelers’ gut when they return home.

A research team from Washington University in the United States and Maastricht University in the Netherlands have examined the presence of antimicrobial resistance (AMR) genes in the human gut microbiome by analyzing fecal samples obtained from 190 Dutch travelers before and after their trips to Eastern Africa, Southern Asia, and Southeastern Asia, and Northern Africa.

Study: Destination shapes antibiotic resistance gene acquisitions, abundance increases, and diversity changes in Dutch travelers. Image Credit: Alpha Tauri 3D Graphics / Shutterstock

The gut microbiome contains bacteria and other organisms that dwell in the human digestive system. The subjects and samples were drawn from a subset of data from the wider COMBAT research, which also looked at AMR.

AMR genes in bacteria evolved spontaneously in bacteria over millennia when they were subjected to antibiotics generated naturally by a few environmental bacteria, but antibiotic misuse and overuse in human medicine and animal agriculture is hastening the process.

Antimicrobial-resistant microorganisms do not react to drugs against which they have evolved resistance.

The scientists discovered an increase in the diversity and amount of AMR genes in fecal samples, including high-risk AMR genes that are impervious to common and last-resort antibiotics (antibiotics that are utilized when other antibiotics do not function), from travelers returning from overseas.

The researchers employed metagenome sequencing of the fecal microbiome to detect AMR genes in the samples by comparing them to a database of familiar AMR genes. They also discovered novel AMR genes by determining whether genes from the samples, when given to an E. coli host, would enable these microbes to develop new antibiotic resistance.

The diversity of AMR genes in the microbiome dramatically increased in people who returned from all destinations, with proof for 56 different AMR genes acquired while traveling. Such diversity was highest in individuals who traveled to Southeast Asia.

AMR genetic diversity was lower among travelers who traveled to the same place, indicating that they shared more AMR genes than with travelers from different places. This suggests that destination-specific AMR genes were picked up by travelers.

A thorough genomic investigation revealed high-risk AMR genes that are impervious to both common and last-resort antibiotics. Six of the 10 high-risk genes found were present after travel but not before, suggesting that they were acquired while traveling.

The mcr-1 gene, for instance, which gives resistance to colistin, a last-resort therapy for illnesses including meningitis and pneumonia, was discovered exclusively in samples collected after travel.

The gene was detected mostly in the microbiome of travelers to Southeast Asia; 18 of 52 (34.6 %) of travelers included in the research who traveled to destinations in the area carried the gene upon their return. The discovery suggests that travelers may have picked up the gene at their destinations.

Some AMR genes were found in fecal samples of the microbiome obtained before travel, and the authors conceded that it is likely that the travelers also disseminated AMR genes to the places they visited. The investigators were unable to determine how the travelers picked up the AMR genes because they lacked samples from the contacts with whom the travelers interacted.

These findings provide strong support that international travel risks spreading antimicrobial resistance globally. Upon returning, travelers’ microbiomes had acquired a significant amount of AMR genes. Many of these genes were high-risk AMR genes, since they confer resistance to commonly used antibiotics.”

Alaric D'Souza, Study Lead Author, Washington University

The authors concluded that understanding how AMR genes migrate from one country to another would help focus on public health interventions to prevent future spread. Upcoming studies may look at the contacts travelers interact with during their trips to learn more about how AMR genes are passed on.

It is vital that we address AMR in lower income countries with high resistance rates and low public health funds. This global approach may not only help the respective countries, but it could also benefit others by reducing the international spread of resistance genes.”

Alaric D'Souza, Study Lead Author, Washington University